1. Field of the Invention
The present invention relates to a seat belt pretensioner which can rapidly pull in a length of a seat belt to tighten the seat belt about a vehicle occupant in case of a crash, thereby restraining and protecting the vehicle occupant.
2. Description of Related Art
In case of a crash, a vehicle occupant is moved forward through a substantial distance before a seat belt is locked by a retractor. A seat belt pretensioner functions to tighten the seat belt and protect the vehicle occupant before the forward movement of the vehicle occupant begins.
Referring to FIG. 1, a seat belt 100 is generally divided into an upper belt part 100A and a lower belt part 100B when viewed from a buckle tongue 110. The upper belt part 100A extends from the shoulder diagonally across the torso to the waist of a vehicle occupant, and the lower belt part 100B extends laterally across the hips to restrain the waist of the vehicle occupant. A conventional seat belt pretensioner 200 shown in FIG. 1 is installed adjacent to a buckle 300. The seat belt pretensioner 200 is connected to the lower belt part 100B through the engagement between the buckle tongue 110 and the buckle 300 to reduce the movement of the waist of the vehicle occupant in case of a crash.
The seat belt pretensioner 200 shown in FIG. 1 is disclosed in Japanese Unexamined Patent Publication No. 2003-146184. The seat belt pretensioner 200 is structured such that a piston (not shown) disposed in a cylinder 210 is connected with the buckle 300 by a wire 220, and a gas generator 240 is arranged in front of the cylinder 210 (in a direction facing the buckle 300). As the piston is fired rearward by the propellant gas generated from the gas generator 240, the wire 220 pulls the buckle 300 and tightens the lower belt part 100B. The gas generator 240 is installed to project vertically with respect to the cylinder 210 so as to avoid interference with the wire 220. In FIG. 1, the unexplained reference numerals 230, 241, 400 and 500 respectively designate a housing, a cap, a retractor, and a center pillar.
The conventional seat belt pretensioner suffers from a drawback in that, since the gas generator 240 is arranged in front of the cylinder 210, an area where the gas generator 240 is placed becomes structurally complicated, the number of parts increases, and the ease of assembly deteriorates. Also, the vertically projecting gas generator 240 interferes with surrounding parts such as a vehicle body, thereby serving as a factor that impedes the miniaturization of the pretensioner.